[Vintage-Audio] What Did They Really Do?

[Gerry Steffens]

Only time for one right now.

Simply, multiplex is the method of broadcasting stereo.  In its simplest
form an fm carrier is modulated with a left plus right signal.  This allows
old FM mono radios to receive both left and right channels as a single mono
signal.

Then a sub-carrier on the FM signal is modulated with a left minus right or
a signed difference signal.

After detection the main carrier signal is added to the sub-carrier signal
giving one a left channel signal with the right channel canceling itself.
The equation follows: (L+R) + (L-R) = 2L.

At the same time the sub-carrier signal is also separately subtracted from
the main channel signal giving a signal of the right channel.  The equation
follows:  (L+R) - (L-R) = 2R.

Works pretty neat.  My son actually did a science fair project on this and
passed the signals from the tuner to two remote audio amplifiers and
speakers using two sets of light bulbs hooked up to amplifier outputs with
lenses focusing the light beams on vacuum photocells each 6 feet remote from
the tuner with its own amplifier.  Nothing very fancy but it blew them away
at the time.  Particularly since all the equipment was vacuum tube gear in
the 1980s.

And yes I first used two stereo equalizers to effectively do my own Dolby B
equivalent.  I also used Dolby C and DBX noise reduction systems a little
later.  They did indeed work to reduce tape hiss, some better than others.
I still infrequently use the two equalizer method to provide the equivalent
of Dolby B with some reel to reel recordings. 

Anyway, off to a town meeting.

Cheers from Minnesota,

Gerry


Collecting & Restoring since 1959
Gerald Steffens P.E.
Oronoco, MN


-----Original Message-----
From: vintage-audio-bounces at mailman.qth.net
[mailto:vintage-audio-bounces at mailman.qth.net] On Behalf Of Duane B.
Fischer, W8DBF
Sent: Thursday, February 24, 2005 6:19 PM
To: vintage-audio at mailman.qth.net
Subject: [Vintage-Audio] What Did They Really Do?


	
Back in the sixties and seventies a number of devices hit the stereo shops
that
were supposed to make listening to FM and FM stereo and reel to reel tapes
much
better. Among them the DBX, Multiplex and others 	
	
What did they 'really' do and how much of those claims were just hype?Did
any of
you actually use them and what are your thoughts?	
	
Duane W8DBF	

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